This invention relates to improvements in a rope traction device used for winding instruments for construction, loading and unloading, and conveying machines including moving scaffolds, elevators and cranes, and particularly is directed to an improvement in the reliability and durability of the rope traction device.
A rope traction device is a type of winding instrument used for construction, loading and unloading, and conveying machines such as moving scaffolds, elevators and cranes, and is capable of moving up and down along a rope with the rope wound around its sheave by only one or a few windings, and without winding the rope around and feeding it from a drum.
An example of a prior art rope traction device used for moving a scaffold up and down to perform work along an exterior wall surface of a building, is shown in FIGS. 3 and 4. This rope traction device includes a frame 1, a drive shaft 2 mounted on the frame 1, a motor 3 provided on the outer periphery of drive shaft 2 through a bearing, and a sheave 4 driven by motor 3. The rope traction device further includes a traction mechanism 6 for holding a rope 5 wound about sheave 4 by one winding, for preventing rope 5 from slipping off sheave 4, and further includes a brake mechanism 7.
Traction mechanism 6 includes an L-shaped pivoting arm 8 provided in the vicinity of a point at which rope 5 is disengaged from sheave 4. A pair of rollers 9, 9 are rotatably mounted at one end of pivoting arm 8 to press rope 5 inwardly from a linearly tightened state thereof. Another pair of rollers 10, 10 are rotatably mounted on a pivoting arm 11 which is pivotally mounted at the other end of pivoting arm 8.
According to this structure, as rope 5 becomes tightened linearly, rollers 9, 9, which are in contact with rope 5, are pushed outwardly by rope 5. Pivoting arm 8 is thereby pivoted in a counterclockwise direction, as viewed in FIG. 4, to cause rope 5 to be pressed by rollers 10, 10 into the groove of sheave 4.
The output shaft of motor 3 is coupled to drive shaft 2 and a wheel 14 of an intermediate shaft 13 is in meshing engagement with a pinion 12 provided on drive shaft 2. A second pinion 15 on intermediate shaft 13 is in meshing engagement with a gear 20 of a brake wheel 19 having a female screw 18 which is in threaded engagement with a male screw 17 of a driven shaft 16. A pinion 21 formed at the end portion of driven shaft 16 is in meshing engagement with a ring gear 22 which is secured to sheave 4 by means of bolts. A flange portion 23 is formed on driven shaft 16 in a manner which opposes brake wheel 19. Linings 24, 24 are provided on opposing surfaces of flange portion 23 and brake wheel 19. A brake disk 26 which can rotate in one direction only through frame 1 and a ratchet 25 are provided between flange portion 23 and brake wheel 19.
When it is desired to elevate the rope traction device by rotating sheave 4 clockwise as viewed in FIG. 4, driven shaft 16 is rotated counterclockwise. Since ratchet 25 is free in this direction, brake wheel 19, with its female screw 18 in threaded engagement with male screw 17 of driven shaft 16, is displaced to the left as viewed in FIG. 3. This occurs by the rotation of brake wheel 19 which presses brake disk 26 against flange portion 23. Thus, brake wheel 19 is rotated integrally with driven shaft 16 to transmit the drive force to sheave 4.
When sheave 4 is rotated counterclockwise, that is, in a direction in which the rope traction device is lowered, brake disk 26 is locked by ratchet 25 and sheave 4 itself is in a loaded state. By the rotation of motor 3, brake wheel 19 is rotated in a direction in which brake wheel 19 is displaced to the right as viewed in FIG. 3. As a result, the rope traction device is lowered due to the load applied to sheave 4 by a distance corresponding to the gap produced in brake disk 26. The rope traction device is lowered by the repeated release and engagement of the brake.
In traction mechanism 6 in which rope 5 is pressed against sheave 4 by the pair of rollers 10, 10 mounted on pivoting arm 11, a bending moment is repeatedly applied to rope 5. This occurs at points of contact with the V-shaped groove of sheave 4 at two positions at which rollers 10, 10 press against rope 5. In addition, rollers 10, 10 tend to slip sideways by a force applied in a transverse direction due to twisting of rope 5. For these reasons, wear occurs in rope 5 and the life of rope 5 is thereby shortened.
Further, as wear occurs in rope 5 and its diameter is thereby reduced, the position of pivoting arm 8 before pivoting is changed. As a result, the pressing force, that is, the traction force obtained by the inward displacement of rollers 9, 9 is changed, resulting instability in the traction force.
It is, therefore, an object of the invention to provide a rope traction device which is capable of producing a large rope pressing force and ensuring a prolonged life of the rope without causing excessive wear.
In brake mechanism 7 in which the braking force is produced by the screw mechanism between brake wheel 19 and driven shaft 16, the force produced by screws 17 and 18 is weak when the load is relatively small. This gives rise to the problem that the grease used for lubricating the component parts such as wheels located near linings 24, 24 contaminates linings 24, 24. The force produced by screws 17 and 18 is too small to force the grease out of linings 24, 24 with the result that the braking force is decreased.
There is another problem with brake mechanism 7. When a large force such as an impact force has been applied to brake mechanism 7, there is the likelihood that the tightening force produced between screws 17 and 18 becomes excessively large, resulting in malfunction of the brake.
In brake mechanism 7 in which release and application of the brake are repeated frequently during lowering of the rope traction device, grease tends to deteriorate due to heat of friction produced in linings 24, 24 when the distance of downward movement of the rope traction device is long. As a result, linings 24, 24 tend to be burnt and the braking efficiency is seriously reduced.
It is therefore another object of the invention to provide a rope traction device capable of producing a stable braking force regardless of magnitude of the load applied to the brake mechanism.